1. Field of the Invention
The present invention relates to a method of spraying a molding die with release agent before molding a package of at least one semiconductor chip.
2. Description of the Related Art
It is possible to facilitate the ejection of molded parts from a molding die by adding sufficient amount of release agent to black resin to be molded for packaging ordinary IC (Integrated Circuit) chips, or LSI (Large Scale Integrated circuit) chips such as memory chips, for example. However, when packaging semiconductor chips for optical applications, such as CCD (Charge Coupled Device) shift registers with transparent resin, if release agent is mixed in this transparent resin, there is a possibility that the transmittance decreases or a faulty image pickup occurs, so that the release agent cannot be contained sufficiently in the resin.
When there is a trace amount of release agent contained in the transparent resin, if packaging is performed by molding this resin, the release characteristics of the release agent are notably poor, resulting in the occurrence of exterior defects such as cracking or delamination in the molded transparent resin. For this reason, it has been a conventional practice to form a release agent layer between the die and the resin by spraying a silicone-containing release agent on the whole surface of the die.
When resin moldings are executed by spraying a silicone-based release agent on the whole surface of the die, the silicone components in the release agent remain in large amounts as foreign substances in the molded resin. More specifically, the resin from the pot flows, while entrapping some of the release agent adhering to the surfaces of the pot, the runner and the gates, and is poured into the cavities. The silicone components of the release agent entrapped in the resin remain as foreign substances in the resin, and those foreign substances act as optical defects when the molded packages are used in an optical system. If resin moldings are made by spraying the whole surfaces of the die with fluorine-based release agent not containing silicone components, the components of the release agent do not remain as foreign substances in the resin. However, fluorine-based release agents of this kind are extremely inferior in release characteristics to silicone-based release agents. Therefore, when a molded part is removed from the die, it is subjected to a tensile stress, and exterior imperfections such as cracking and delamination occur.